U.S. patent application number 10/366276 was filed with the patent office on 2004-08-26 for method and device for controlling voltage provided to a suspended particle device.
This patent application is currently assigned to Research Frontiers Incorporated. Invention is credited to Harary, Joseph M., Malvino, Albert P., Saxe, Robert L..
Application Number | 20040165251 10/366276 |
Document ID | / |
Family ID | 32849730 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040165251 |
Kind Code |
A1 |
Malvino, Albert P. ; et
al. |
August 26, 2004 |
Method and device for controlling voltage provided to a suspended
particle device
Abstract
A voltage controlling device includes an AC terminal receiving
an AC voltage signal, a voltage dividing device adapted to divide
the AC voltage signal into a plurality of distinct voltage signals
within a predetermined range, a controller adapted to control the
voltage dividing device to provide a selected voltage level based
on voltage level information and an SPD terminal for providing the
selected voltage level to a suspended particle device. An input
device may be provided to allow a user to input the voltage level
information. A photocell that monitors a light level at the
suspended particle device may provide light level information as
the voltage level information. A separate AC power supply may also
be provided. The controller may also monitor an SPD load voltage to
control the selected voltage level provided to the SPD terminal and
the suspended particle device in order to prevent shocking of a
user.
Inventors: |
Malvino, Albert P.; (Corpus
Christi, TX) ; Saxe, Robert L.; (New York, NY)
; Harary, Joseph M.; (Brooklyn, NY) |
Correspondence
Address: |
Mark A Farley
Ostrolenk Faber Gerb & SOffen LLP
1180 Avenue of the Americas
New York
NY
10036-8403
US
|
Assignee: |
Research Frontiers
Incorporated
|
Family ID: |
32849730 |
Appl. No.: |
10/366276 |
Filed: |
February 13, 2003 |
Current U.S.
Class: |
359/296 |
Current CPC
Class: |
G02F 1/172 20130101;
G02B 26/004 20130101 |
Class at
Publication: |
359/296 |
International
Class: |
G02B 026/00 |
Claims
What is claimed is:
1. A voltage controlling device for controlling voltage provided to
at least one suspended particle device (SPD) which comprises: an AC
terminal adapted to receive an AC voltage at a specific frequency;
a voltage dividing device adapted to divide the AC voltage into a
plurality of distinct voltage values within a predetermine range; a
controller adapted to control the voltage dividing device to
provide a selected voltage value based on voltage level
information; and an SPD terminal adapted to provide the selected
voltage value to the SPD device.
2. The voltage controlling device of claim 1, wherein the voltage
dividing device further comprises: a capacitor array including a
plurality of capacitors where each capacitor in the capacitor array
has a predetermined capacitance; and a switch array, connecting
each capacitor of the capacitor array to the SPD terminal such that
each switch of the switch array connects one capacitor of the
capacitor array to the SPD terminal, wherein the controller
controls the switches of the switch array to connect at least one
of the capacitors of the capacitor array to the SPD terminal based
on the voltage level information.
3. The voltage controlling device of claim 2, wherein the capacitor
array includes 8 capacitors, and the switch array includes 8
switches, respectively connecting each of the eight capacitors to
the SPD terminal, such that the voltage dividing device is capable
of providing a total of 256 different voltages to the SPD
terminal.
4. The voltage controlling device of claim 1, wherein the
predetermined range of distinct voltages provided by the voltage
dividing device is sufficiently large to provide a maximum voltage
to the SPD terminal sufficient to operate a suspended particle
device of a corresponding size.
5. The voltage controlling device of claim 1, further comprising an
input device adapted to provide the voltage level information from
a user of the voltage controlling device.
6. The voltage controlling device of claim 1, wherein the
controller monitors an SPD voltage provided to the SPD terminal and
controls the voltage dividing device to provide zero voltage to the
SPD terminal after the SPD voltage drops a predetermined amount
below a predetermined level.
7. The voltage controlling device of claim 1, further comprising an
alarm, wherein the controller provides an alarm signal that
activates the alarm after the SPD voltage exceeds a predetermined
level by a predetermined amount.
8. The voltage controlling device of claim 7, wherein the
predetermined level is based on an average value of the SPD voltage
over a predetermined period of time.
9. The voltage controlling device of claim 5, wherein the
predetermined level is stored in a memory of the controller.
10. The voltage controlling device of claim 1, further comprising a
photo detector adapted to monitor a level of light at the suspended
particle device, wherein the level of light at the suspended
particle device is used as the voltage level information utilized
by the controller.
11. The voltage controlling device of claim 1 further comprising:
an AC power supply providing an AC voltage at a low frequency to
the AC terminal.
12. The voltage controlling device of claim 11, wherein the AC
power supply provides an AC voltage with a frequency of at least 15
hertz.
13. The voltage controlling device of claim 11, wherein the AC
power supply comprises: an AC/DC converter converting an AC voltage
signal of a predetermine frequency into a DC voltage signal; a DC
motor operated by the DC voltage signal; and a generator connected
to the DC motor to provide the AC voltage signal at the low
frequency.
14. The voltage controlling device of claim 11, wherein the AC
power supply further comprises: a plurality of solar cells
connected in parallel; at least one rechargeable battery adapted to
provide a DC voltage signal; a converter, adapted to convert a DC
voltage signal of the at least one rechargeable battery into the AC
voltage signal with the low frequency; wherein the at least one
rechargeable battery is recharged by a recharging voltage signal
supplied by the plurality of solar cells.
15. The voltage controlling device of claim 14, wherein the AC
power supply is mounted in a movable support in which the suspended
particle device is mounted, such that the AC power supply moves
with the suspended particle device.
16. The voltage controlling device of claim 1, wherein the
suspended particle device includes: a first conducting layer; a
second conducting layer; and an emulsion including a plurality of
suspended particles which align in a predetermined pattern when
exposed to an electric field, where the emulsion is positioned
between the first conducting layer and the second conducting layer,
and wherein a first conducting bus connecting the first conducting
layer to the SPD terminal and a second conducting bus connecting
the second conducting layer to the SPD terminal are positioned on
one edge of the suspended particle device.
17. The voltage controlling device of claim 16, wherein a length of
the one edge of the suspended particle device is less than a length
of another edge of the suspended particle device such that the
suspended particle device is substantially rectangular in
shape.
18. The voltage controlling device of claim 16, wherein a bus
length of the first conducting bus and the second conducting bus is
less than a length of the one edge of the suspended particle
device.
19. A voltage controlling device for controlling voltage provided
to at least one suspended particle device which comprises: an AC
terminal adapted to receive an AC voltage at a specific frequency;
an SPD terminal adapted to provide a selected AC voltage value to
the suspended particle device a capacitor array including a
plurality of capacitors where each capacitor in the capacitor array
has a predetermined capacitance; a switch array, connecting each
capacitor of the capacitor array to the SPD terminal such that each
switch of the switch array connects one capacitor of the capacitor
array to the SPD terminal; and a controller adapted to control the
switches of the switch array to connect at least one of the
capacitors of the capacitor array to the SPD terminal based on
voltage level information, such that a plurality of distinct
voltage values within a predetermined range are selectively
provided to the SPD terminal.
20. A method of controlling voltage provided to a suspended
particle device, which method comprises: receiving an AC voltage
signal at a specific frequency; dividing the AC voltage signal into
a plurality of distinct voltage levels within a predetermined
range; controlling the dividing step to provide a selected voltage
level of the plurality of distinct voltage levels to an SPD
terminal connected to the suspended particle device based on
voltage level information.
21. The method of claim 20, wherein the dividing step further
comprises: providing a capacitor array including a plurality of
capacitors, each said capacitor having a predetermined capacitance;
connecting each capacitor of the capacitor array to the SPD
terminal via a switch of a switch array, wherein a number of
switches in the switch array is the same as a number of capacitors
in the capacitor array; and controlling the switch array and the
capacitor array such that at least one capacitor of the capacitor
array is connected to the suspended particle device to provide the
selected voltage level.
22. The method of claim 21, wherein the connection step includes
connecting eight capacitors in the capacitor array via eight
switches in the switch array to the SPD terminal, such that a total
of 256 selected voltage levels are provided to the SPD
terminal.
23. The method of claim 20, wherein the predetermined range of
distinct voltages is sufficiently large to provide a maximum
voltage to the SPD terminal sufficient to operate a suspended
particle device of a corresponding size.
24. The method of claim 20, further comprising: inputting the
voltage level information via an input device for use in the
controlling step.
25. The method of claim 20 further comprising, monitoring an SPD
voltage level provided to the SPD terminal; determining a normal
SPD voltage level based on an average SPD voltage level over a
predetermined period of time; and comparing the SPD voltage level
to the normal SPD voltage level; wherein the controlling step
includes providing zero voltage to the SPD terminal after the SPD
voltage level drops a predetermined amount below the normal SPD
voltage level.
26. The method of claim 25, further comprising: generating an alarm
signal to activate an alarm after the SPD voltage exceeds the
normal SPD voltage by a predetermined amount.
27. The method of claim 25, wherein the normal SPD voltage level is
stored in a memory.
28. The method of claim 20, further comprising: detecting a light
level at the suspended particle device; and generating a light
level signal wherein the light level signal is used as the voltage
level information in the controlling step.
29. The method of claim 20, further comprising: generating the AC
voltage signal at a low frequency.
30. The method of claim 29, wherein the AC voltage signal has a
frequency of at least 15 hertz.
31. The method of claim 30, wherein the generating step further
comprises: converting an AC voltage signal of a predetermined
frequency into a DC voltage signal; driving a DC motor with the DC
voltage signal; and generating an AC voltage signal having the low
frequency via a generator powered by the DC motor.
32. The method of claim 30, wherein the generating step further
includes: connecting a plurality of solar cells in series to at
least one rechargeable battery; converting a DC voltage signal from
the at least one rechargeable battery into an AC voltage signal
with the low frequency with a DC/AC converter; and recharging the
at least one rechargeable battery with a recharging voltage signal
supplied by the plurality of solar cells.
33. The method of claim 32, further comprising: mounting the solar
cells, the DC/AC converter and the at least one rechargeable
battery in a movable support in which the suspended particle device
is mounted.
34. The method of claim 20, wherein construction of the suspended
particle device comprises: providing a first conducting layer;
providing a second conducting layer; positioning an emulsion
including a plurality of suspended particles, which align in a
predetermined pattern when exposed to an electric field between the
first conducting layer and the second conducting layer; positioning
a first conducting bus on the first connecting layer to connect the
first conducting layer to the SPD terminal positioning a second
conducting bus on the second conducting layer to connect the second
conducting layer to the SPD terminal, such that the first
conducting bus and the second conducting bus are positioned on one
edge of the suspended particle device.
35. The method of claim 34, wherein a length of the one edge of the
suspended particle device is less than a length of another edge of
the suspended particle device such that the suspended particle
device is substantially rectangular in shape.
36. The method of claim 34, wherein a bus length of the first
conducting bus and the second conducting bus is less than a length
of the one edge of the suspended particle device.
37. A system of controlling voltage which comprises: a voltage
controlling device, wherein the voltage controlling device
includes; an AC terminal adapted to receive an AC voltage at a
specific frequency; a voltage dividing device adapted to divide the
AC voltage into a plurality of distinct voltage values within a
predetermine range; a controller adapted to control the voltage
dividing device to provide a selected voltage value based on
voltage level information; an SPD terminal device adapted to
receive the selected voltage value; and a suspended particle
device, wherein the suspended particle device includes: a first
conducting layer; a second conducting layer; an emulsion including
a plurality of suspended particles, which align in a predetermined
pattern when exposed to an electric field, where the emulsion
positioned between the first conducting layer and the second
conducting layer, a first connecting bus connecting the first
conducting layer to the SPD terminal; and a second conducting bus
connecting the second conducting layer to the SPD terminal.
38. The system of claim 37, wherein the voltage dividing device
further comprises: a capacitor array including a plurality of
capacitors where each capacitor in the capacitor array has a
predetermined capacitance; and a switch array, connecting the
capacitor array to the SPD terminal such that each switch of the
switch array connects one capacitor of the capacitor array to the
SPD terminal, wherein the controller controls the switches of the
switch array to connect at least one of the capacitors of the
capacitor array to the SPD terminal based on the voltage level
information.
39. The system of claim 38, wherein the capacitor array includes 8
capacitors, and the switch array includes 8 switches, respectively
connecting each of the eight capacitors to the SPD terminal, such
that the voltage dividing device is capable of providing a total of
256 different voltages to the SPD terminal.
40. The system of claim 37, wherein the predetermined range of
distinct voltages provided by the voltage dividing device is
sufficiently large to provide a maximum voltage to the SPD terminal
sufficient to operate a suspended particle device of a
corresponding size.
41. The system of claim 37, wherein the voltage controlling device
further comprises: an input device adapted to provide the voltage
level information from a user of the system.
42. The system of claim 37, wherein the controller monitors an SPD
voltage provided to the SPD terminal and controls the voltage
dividing device to provide zero voltage to the SPD terminal after
the SPD voltage drops a predetermined amount below a predetermined
level.
43. The system of claim 42, wherein the voltage controlling device
further comprises: an alarm, wherein the controller provides an
alarm signal that activates the alarm after the SPD voltage exceeds
the predetermined level by a predetermined amount.
44. The system of claim 42, wherein the predetermined level is
based on an average value of the SPD voltage over a predetermined
period of time.
45. The system of claim 42, wherein the predetermined level is
stored in a memory of the controller.
46. The system of claim 37, wherein the voltage controlling device
further comprises: a photo detector adapted to monitor a level of
light at the suspended particle device, wherein the level of light
at the suspended particle is used as the voltage level information
utilized by the controller to control the voltage provided to the
SPD terminal by the voltage dividing device.
47. The system of claim 37 wherein the voltage controlling device
further comprises: an AC power supply providing an AC voltage
signal at a low frequency to the AC terminal.
48. The system of claim 47, wherein the AC power supply provides an
AC voltage signal with a frequency of at least 15 hertz.
49. The system of claim 47, wherein the AC power supply comprises:
an AC/DC converter converting an AC voltage signal of a
predetermine frequency into a DC voltage signal; a DC motor
operated by the DC voltage signal; and a generator connected to the
DC motor to provide an AC voltage signal at the low frequency.
50. The system of claim 47, wherein the AC power supply further
comprises: a plurality of solar cells connected in parallel; at
least one rechargeable battery adapted to provide a DC voltage
signal; a converter, adapted to convert the DC voltage signal of
the battery into an AC voltage signal with the low frequency;
wherein the at least one rechargeable battery is recharged by a
recharging voltage signal supplied by the plurality of solar
cells.
51. The system of claim 50, wherein the AC power supply is mounted
in a movable support in which the suspended particle device is
mounted, such that the AC power source moves with the suspended
particle device.
52. The system of claim 37, wherein the first connecting bus and
the second connecting bus of the suspended particle device are
connected to the first conducting layer and the second conducting
layer, respectively, on one edge of the suspended particle
device.
53. The system of claim 52, wherein a length of the one edge of the
suspended particle device is less than a length of another edge of
the suspended particle device such that the suspended particle
device is substantially rectangular in shape.
54. The system of claim 52, wherein a bus length of the first
connecting bus and the second connecting bus, respectively, is less
than a length of the one edge of the suspended particle device.
Description
FIELD OF THE INVENTION
[0001] The present application relates to a power-efficient and
low-cost method and device for controlling an AC voltage applied to
a suspended particle device (SPD). The present application also
relates to methods and devices for shock prevention, detecting
forced entry, and reducing the manufacturing costs of SPD film.
BACKGROUND OF THE INVENTION
[0002] Light valves have been in use for more than sixty years for
the modulation of light. As used herein, a light valve is defined
as a cell formed of two walls that are spaced apart by a small
distance, at least one wall being transparent, the walls having
electrodes thereon, usually in the form of transparent,
electrically conductive coatings. The cell contains a
light-modulating element (sometimes herein referred to as an
"activatable material"), which may be either a liquid suspension of
particles, or a plastic film in which droplets of a liquid
suspension of particles are distributed.
[0003] The liquid suspension (sometimes herein referred to as "a
liquid light valve suspension" or "a light valve suspension")
comprises small, an isometrically shaped particles suspended in a
liquid suspending medium. In the absence of an applied electrical
field, the particles in the liquid suspension assume random
positions due to Brownian movement, and hence a beam of light
passing into the cell is reflected, transmitted or absorbed,
depending upon the cell structure, the nature and concentration of
the particles, and the energy content of the light. The light valve
is thus relatively dark in the OFF state. However, when an electric
field is applied through the liquid light valve suspension in the
light valve, the particles become aligned and for many suspensions
most of the light can pass through the cell. The light valve is
thus relatively transparent in the ON state. Light valves of the
type described herein are also known as "suspended particle
devices" or "SPDs." More generally, the term suspended particle
device, as used herein, refers to any device in which suspended
particles align to allow light to pass through the device when an
electric field is applied.
[0004] Light valves have been proposed for use in numerous
applications including, e.g., alphanumeric and graphic displays;
television displays; filters for lamps, cameras, optical fibers,
and windows, sunroofs, sunvisors, eyeglasses, goggles and mirrors
and the like, to control the amount of light passing therethrough
or reflected therefrom as the case may be. As used herein the term
"light" generally refers to visible electromagnetic radiation, but
where applicable, "light" can also comprise other types of
electromagnetic radiation such as, but not limited to, infrared
radiation and ultraviolet radiation.
[0005] For many applications, as would be well understood in the
art it is preferable for the activatable material, i.e., the light
modulating element, to be a plastic film rather than a liquid
suspension. For example, in a light valve used as a variable light
transmission window, a plastic film, in which droplets of liquid
suspension are distributed, is preferable to a liquid suspension
alone because hydrostatic pressure effects, e.g., bulging,
associated with a high column of liquid suspension, can be avoided
through use of a film, and the risk of possible leakage can also be
avoided. Another advantage of using a plastic film is that in a
plastic film, the particles are generally present only within very
small droplets, and hence do not noticeably agglomerate when the
film is repeatedly activated with a voltage.
[0006] As used herein, the terms "SPD film" or "light valve film"
mean at least one film or sheet comprising a suspension of
particles used or intended for use by itself or as part of a light
valve. The light valve film or SPD film includes either: (a) a
suspension of particles dispersed throughout a continuous liquid
phase enclosed within one or more rigid or flexible solid films or
sheets, or (b) a discontinuous phase of a liquid comprising
dispersed particles, the discontinuous phase being dispersed
throughout a continuous phase of a rigid or flexible solid film or
sheet. The light valve film or SPD film may also include one or
more other layers such as, without limitation, a film, coating or
sheet, or combination thereof, which may provide the light valve
film or SPD film with (1) scratch resistance (2) protection from
ultraviolet radiation (3) reflection of infrared energy, and/or (4)
electrical conductivity for transmitting an applied electric or
magnetic field to the activatable material.
[0007] U.S. Pat. No. 5,409,734 illustrates an example of a type of
light valve film that is formed by phase separation from a
homogeneous solution. Light valve films may be made by
cross-linking emulsions such as those described in U.S. Pat. Nos.
5,463,491 and 5,463,492, both of which are assigned to the assignee
of the present invention.
[0008] The following is a brief description of liquid light valve
suspensions known in the art, although the invention is not limited
to the use of only such suspensions.
[0009] 1. Liquid Suspending Media and Stabilizers
[0010] A liquid light valve suspension for use with the invention
may be any liquid light valve suspension known in the art and may
be formulated according to techniques well known to one skilled in
the art. The term "liquid light valve suspension", as used herein,
means a "liquid suspending medium" in which a plurality of small
particles is dispersed. The "liquid suspending medium" includes one
or more non-aqueous, electrically resistive liquids in which there
is preferably dissolved at least one type of polymeric stabilizer,
which acts to reduce the tendency of the particles to agglomerate
and to keep them dispersed and in suspension.
[0011] Liquid light valve suspensions useful in the present
invention may include any of the liquid suspending media previously
proposed for use in light valves for suspending the particles.
Liquid suspending media known in the art which are useful herein
include, but are not limited to the liquid suspending media
disclosed in U.S. Pat. Nos. 4,247,175 and 4,407,565. In general, at
least one of the liquid suspending medium and the polymeric
stabilizer dissolved therein is chosen in a manner known in the art
so as to maintain the suspended particles in gravitational
equilibrium.
[0012] The polymeric stabilizer, when employed, can be a single
solid polymer that bonds to the surface of the particles, but which
also dissolves in the non-aqueous liquid or liquids of the liquid
suspending medium. Alternatively, two or more solid polymeric
stabilizers may serve as a polymeric stabilizer system. For
example, the particles can be coated with a first type of solid
polymeric stabilizer such as nitrocellulose which, in effect,
provides a plain surface coating for the particles, after which
they are re-coated with one or more additional types of solid
polymeric stabilizer that bond to or associate with the first type
of solid polymeric stabilizer and which also dissolve in the liquid
suspending medium to provide dispersion and steric protection for
the particles. Also, liquid polymeric stabilizers may be used to
advantage, especially in SPD light valve films, as described in
U.S. Pat. No. 5,463,492.
[0013] 2. Particles
[0014] Inorganic and organic particles may be incorporated into a
light valve suspension useful in forming a switchable suspended
particle device. Such particles may be either light-absorbing or
light-reflecting in the visible portion of the electromagnetic
spectrum. For some particular applications the particles can be
reflective at infrared wavelengths.
[0015] Conventional SPD light valves have generally employed
polyhalide particles of colloidal size, that is the particles
generally have a largest dimension averaging about 1 micron or
less. As used herein, the term "colloidal", when referring to
particle size, shall have the meaning given in the preceding
sentence. Preferably, most polyhalide or other particles used or
intended for use in an SPD light valve suspension used in
accordance with the invention will have a largest dimension which
averages less than one-half of the wavelength of blue light, i.e.,
less than 2000 Angstroms, to keep light scatter extremely low. As
used herein, the term "anisometric", which refers to particle
shape, means that at least one dimension is larger than another.
Typically, anisometric particles (sometimes referred to as
particles which are anisometrically shaped), are desirable in an
SPD light valve suspension so that the particles will block less
light when the suspension is activated than when it is unactivated.
For some suspensions the reverse is true, however. Desirable
anisometric shapes for the particles include, without limitation
thereto, particles shaped like rods, cylinders, plates, flakes,
needles, blades, prisms, and other shapes known in the art.
[0016] A detailed review of prior art polyhalide particles is found
in "The Optical Properties and Structure of Polyiodides" by D. A.
Godina and G. P. Faerman, published in "The Journal of General
Chemistry", U.S.S.R. Vol. 20, pp. 1005-1016 (1950).
[0017] Herapathite, for example, is defined as a quinine bisulfate
polyiodide, and its formula is given under the heading "quinine
iodsulfate" as
4C.sub.20H.sub.24N.sub.2O.sub.2.3H.sub.2SO.sub.4.2HI.I.sub-
.4.6H.sub.2O in The Merck Index, 10.sup.th Ed. (Merck & Co.,
Inc., Rahway, N.J.). In polyiodide compounds, the iodide anion is
thought to form chains and the compounds are strong light
polarizers. See U.S. Pat. No. 4,877,313 and Teitelbaum et al. JACS
100 (1978), pp. 3215-3217. The term "polyhalide" is used herein to
mean a compound such as a polyiodide, but wherein at least some of
the iodide anion may be replaced by another halide anion. More
recently, improved polyhalide particles for use in light valves
have been proposed in U.S. Pat. Nos. 4,877,313, 5,002,701,
5,093,041 and 5,516,463. These "polyhalide particles" are formed by
reacting organic compounds, usually containing nitrogen, with
elemental iodine and a hydrohalide acid or an ammonium halide,
alkali metal halide or alkaline earth metal halide.
[0018] For some applications, however, it may be desirable to use
non-polyhalide particles in light valve suspensions and films,
especially where the stability of the material composing the
particles is known to be excellent.
[0019] Regardless of the type of suspended particle device used, it
is necessary to have a method and/or means of producing and varying
the AC voltage applied to the suspended particle device, which may
be referred to as an SPD load, from 0V to a maximum voltage that is
acceptable for the specific SPD application. For the purposes of
the present disclosure the term SPD load includes SPD films, SPD
light valves, and all other SPD products that rely on the
application of an electric field to control the orientation of
suspended particles. Where the SPD load utilizes an SPD film, the
voltage that produces maximum light transmission in the SPD load is
a function of SPD film thickness and other properties. Since the
light transmission of the SPD load is a nonlinear function of
voltage, i.e., increasing rapidly at lower voltages and slowly at
high voltages, a design compromise can be made by defining a
maximum acceptable voltage which provides a sufficiently clear
state of the SPD load, currently in the 30 to 60 V rms region. In
this discussion, 60 V rms will be used as the AC voltage that
produces an acceptable clear state with the understanding the newer
SPD films may be developed that produce an almost clear state with
less than 30 V rms.
[0020] Although providing a maximum voltage of 0 to 60 V rms is
suitable for most SPD loads, the SPD load current shows a large
variation because of all the possible configurations and sizes of
SPD loads. For instance, a single SPD window can vary in size from
as little as 1 square foot to as much as 32 square feet or more. In
addition, multiple panels of 8 ft.times.4 ft windows or larger can
aggregate hundreds or even thousands of square feet. For these
larger SPD loads, there are advantages in generating the AC voltage
for the SPD loads, which will be discussed in further detail below.
Furthermore, the busses (also known as bus bars) through which
electricity is supplied to the SPD loads may be optimized to reduce
their manufacturing costs. All of these improvements contribute to
a highly efficient and minimum cost system for controlling voltages
across SPD loads.
[0021] Unless otherwise indicated, the following will be assumed
throughout this discussion:
[0022] Voltage for almost clear state=60 V rms at 60 Hz
[0023] Capacitance per square foot=40 nF (of the SPD film)
[0024] Resistance per square=350 ohms (of the SPD film)
[0025] Based on the foregoing assumptions, a voltage controller for
an SPD load preferably delivers a load current of 0.905 mA for an
SPD load of 1 square foot up to 28.8 mA for an SPD load of 32
square feet. As a conservative approximation, 1 mA per square foot
will be used as a guideline. For instance, an office building with
40 panels of 8 ft by 4 ft windows has a film area of 1280 square
feet. In such a case, the current demand is approximately 1.28 A at
60 V and 60 Hz to attain an almost clear state for all the windows.
Although future developments in SPD film may alter the
voltage-current-power requirements of SPD film, the voltage
controlling device of the present application will accommodate a
wide range of film characteristics.
[0026] Currently existing voltage controlling devices commonly use
a transformer and/or potentiometer to provide and vary the AC
voltage provided to the SPD load. Transformers can be used to step
down voltages if desired, while potentiometers allow for variations
of voltages through a range of values. Transformers, however, tend
to be rather expensive and also reduce efficiency of the voltage
controlling device due to coil losses and core losses inherent in
the transformer.
[0027] One example of a currently existing voltage control device
is described in U.S. Pat. No. 5,764,402 which relates to an optical
cell control system that includes a first oscillator circuit
supplied by a low voltage power source and including a primary
winding of an induction coil and a secondary resonant circuit that
includes the optical cell and a secondary winding of the induction
coil. The second circuit includes the inductance of the secondary
winding and the optical cell. The induction coil provides a weak
coupling between the primary and secondary windings. The resonant
circuit provides a large over-voltage coefficient and good
stability.
[0028] One problem encountered in traditional voltage controlling
devices is that potentiometers provide a continuous range of
voltage values between a minimum value and a maximum value such
that a slight adjustment to the potentiometer results in a slight
change in voltage applied to the SPD load and a corresponding
slight increase in the clarity of the SPD load. Since
potentiometers are resistive circuit elements, power losses in
potentiometers tend to be rather high. In addition, the fine
control provided by the potentiometer is unnecessary in an SPD
application. The human eye is not able to detect slight variations
in clarity of the SPD load, thus the continuous range of voltages
provided by the potentiometer which provide for minute increases in
clarity of the SPD load are unnecessary. Thus, traditional voltage
controlling devices are rather inefficient and provide little
observable benefit in controlling clarity of the SPD load.
[0029] Safety is also a concern in the voltage controlling device.
While SPD loads commonly use relatively small currents, even these
small currents could be hazardous to a user who is exposed to them.
For example, if an SPD window were to crack, the current conducting
layer may be exposed. If one were to contact the exposed current
conducting layer and inadvertently provide a path to ground, the
individual may receive a shock. Traditional current controlling
devices typically utilize a ground fault circuit interrupt (GFCI)
which cuts off current to the SPD load if an unintended ground path
develops. GFCI's, however tend to be somewhat expensive and may not
guard against another shock risk in SPD loads. For example, where
an SPD window is pierced by a sharp object, a user may
inadvertently provide a path between the two conducting layers
directly which may result in a shock to the user. Thus, it would be
advantageous to provide a voltage controlling device which avoids
these problems at a low cost.
[0030] Therefore, it is desirable to provide a voltage controlling
method and device that provide efficient and low cost voltage
control while avoiding the problems discussed above.
SUMMARY OF THE INVENTION
[0031] A voltage controlling device for controlling voltage
provided to at least one suspended particle device (SPD) which
includes an AC terminal adapted to receive an AC voltage at a
specific frequency, a voltage dividing device adapted to divide the
AC voltage into a plurality of distinct voltage values within a
predetermine range a controller adapted to control the voltage
dividing device to provide a selected voltage value based on
voltage level information and an SPD terminal adapted to provide
the selected voltage value to the SPD device.
[0032] The voltage dividing device may include a capacitor array
including a plurality of capacitors where each capacitor in the
capacitor array has a predetermined capacitance and a switch array,
connecting each capacitor of the capacitor array to the SPD
terminal such that each switch of the switch array connects one
capacitor of the capacitor array to the SPD terminal, wherein the
controller controls the switches of the switch array to connect at
least one of the capacitors of the capacitor array to the SPD
terminal based on the voltage level information. The capacitor
array may include 8 capacitors and the switch array may include 8
switches, respectively connecting each of the eight capacitors to
the SPD terminal, such that the voltage dividing device is capable
of providing a total of 256 different voltages to the SPD
terminal.
[0033] The predetermined range of distinct voltages provided by the
voltage dividing device may be sufficiently large to provide a
maximum voltage to the SPD terminal sufficient to operate a
suspended particle device of a corresponding size.
[0034] The voltage controlling device may include an input device
adapted to provide the voltage level information from a user of the
voltage controlling device.
[0035] The controller may monitor an SPD voltage provided to the
SPD terminal and control the voltage dividing device to provide
zero voltage to the SPD terminal after the SPD voltage drops a
predetermined amount below a predetermined level. The voltage
controlling device may include an alarm, wherein the controller may
provide an alarm signal that activates the alarm after the SPD
voltage exceeds a predetermined level by a predetermined amount.
The predetermined level may be based on an average value of the SPD
voltage over a predetermined period of time. The predetermined
level may be stored in a memory of the controller.
[0036] The voltage controlling device may include a photo detector
adapted to monitor a level of light at the suspended particle
device, wherein the level of light at the suspended particle device
is used as the voltage level information utilized by the
controller.
[0037] The voltage controlling device may include an AC power
supply providing an AC voltage at a low frequency to the AC
terminal. The AC power supply may provide an AC voltage with a
frequency of at least 15 hertz. The AC power supply may include an
AC/DC converter converting an AC voltage signal of a predetermine
frequency into a DC voltage signal, a DC motor operated by the DC
voltage signal and a generator connected to the DC motor to provide
the AC voltage signal at the low frequency.
[0038] The AC power supply may further include a plurality of solar
cells connected in parallel, at least one rechargeable battery
adapted to provide a DC voltage signal and a converter, adapted to
convert a DC voltage signal of the at least one rechargeable
battery into the AC voltage signal with the low frequency; wherein
the at least one rechargeable battery is recharged by a recharging
voltage signal supplied by the plurality of solar cells.
[0039] The AC power supply may be mounted in a movable support in
which the suspended particle device is mounted, such that the AC
power supply moves with the suspended particle device.
[0040] The suspended particle device may include a first conducting
layer, a second conducting layer and an emulsion including a
plurality of suspended particles which align in a predetermined
pattern when exposed to an electric field, where the emulsion is
positioned between the first conducting layer and the second
conducting layer, and wherein a first conducting bus connecting the
first conducting layer to the SPD terminal and a second conducting
bus connecting the second conducting layer to the SPD terminal are
positioned on one edge of the suspended particle device.
[0041] The length of the one edge of the suspended particle device
may be less than a length of another edge of the suspended particle
device such that the suspended particle device is substantially
rectangular in shape.
[0042] The bus length of the first conducting bus and the second
conducting bus may be less than a length of the one edge of the
suspended particle device.
[0043] A voltage controlling device for controlling voltage
provided to at least one suspended particle device includes an AC
terminal adapted to receive an AC voltage at a specific frequency,
an SPD terminal adapted to provide a selected AC voltage value to
the suspended particle device, a capacitor array including a
plurality of capacitors where each capacitor in the capacitor array
has a predetermined capacitance, a switch array, connecting each
capacitor of the capacitor array to the SPD terminal such that each
switch of the switch array connects one capacitor of the capacitor
array to the SPD terminal and a controller adapted to control the
switches of the switch array to connect at least one of the
capacitors of the capacitor array to the SPD terminal based on
voltage level information, such that a plurality of distinct
voltage values within a predetermined range are selectively
provided to the SPD terminal.
[0044] A method of controlling voltage provided to a suspended
particle device includes receiving an AC voltage signal at a
specific frequency, dividing the AC voltage signal into a plurality
of distinct voltage levels within a predetermined range and
controlling the dividing step to provide a selected voltage level
of the plurality of distinct voltage levels to an SPD terminal
connected to the suspended particle device based on voltage level
information.
[0045] The dividing step may include providing a capacitor array
including a plurality of capacitors, each said capacitor having a
predetermined capacitance, connecting each capacitor of the
capacitor array to the SPD terminal via a switch of a switch array,
wherein a number of switches in the switch array is the same as a
number of capacitors in the capacitor array and controlling the
switch array and the capacitor array such that at least one
capacitor of the capacitor array is connected to the suspended
particle device to provide the selected voltage level.
[0046] The connection step may include connecting eight capacitors
in the capacitor array via eight switches in the switch array to
the SPD terminal, such that a total of 256 selected voltage levels
are provided to the SPD terminal.
[0047] The predetermined range of distinct voltages may be
sufficiently large to provide a maximum voltage to the SPD terminal
sufficient to operate a suspended particle device of a
corresponding size.
[0048] The method of controlling voltage provided to a suspended
particle device may further include inputting the voltage level
information via an input device for use in the controlling step.
The method may further include monitoring an SPD voltage level
provided to the SPD terminal, determining a normal SPD voltage
level based on an average SPD voltage level over a predetermined
period of time and comparing the SPD voltage level to the normal
SPD voltage level, wherein the controlling step may include
providing zero voltage to the SPD terminal after the SPD voltage
level drops a predetermined amount below the normal SPD voltage
level. The method may further include generating an alarm signal to
activate an alarm after the SPD voltage exceeds the normal SPD
voltage by a predetermined amount. The normal. SPD voltage level is
stored in a memory.
[0049] The method may include detecting a light level at the
suspended particle device and generating a light level signal
wherein the light level signal is used as the voltage level
information in the controlling step.
[0050] The method may include generating the AC voltage signal at a
low frequency. The AC voltage signal preferably has a frequency of
at least 15 hertz.
[0051] The generating step may further include converting an AC
voltage signal of a predetermined frequency into a DC voltage
signal, driving a DC motor with the DC voltage signal and
generating an AC voltage signal having the low frequency via a
generator powered by the DC motor.
[0052] The generating step may include connecting a plurality of
solar cells in series to at least one rechargeable battery,
converting a DC voltage signal from the at least one rechargeable
battery into an AC voltage signal with the low frequency with a
DC/AC converter and recharging the at least one rechargeable
battery with a recharging voltage signal supplied by the plurality
of solar cells.
[0053] The method may also include mounting the solar cells, the
DC/AC converter and the at least one rechargeable battery in a
movable support in which the suspended particle device is
mounted.
[0054] Construction of the suspended particle device may include
providing a first conducting layer, providing a second conducting
layer, positioning an emulsion including a plurality of suspended
particles, which align in a predetermined pattern when exposed to
an electric field between the first conducting layer and the second
conducting layer, positioning a first conducting bus on the first
connecting layer to connect the first conducting layer to the SPD
terminal and positioning a second conducting bus on the second
conducting layer to connect the second conducting layer to the SPD
terminal, such that the first conducting bus and the second
conducting bus are positioned on one edge of the suspended particle
device.
[0055] The length of the one edge of the suspended particle device
may be less than a length of another edge of the suspended particle
device such that the suspended particle device is substantially
rectangular in shape.
[0056] The bus length of the first conducting bus and the second
conducting bus may be less than a length of the one edge of the
suspended particle device.
[0057] A system of controlling voltage includes a voltage
controlling device, wherein the voltage controlling device includes
an AC terminal adapted to receive an AC voltage at a specific
frequency, a voltage dividing device adapted to divide the AC
voltage into a plurality of distinct voltage values within a
predetermine range a controller adapted to control the voltage
dividing device to provide a selected voltage value based on
voltage level information, an SPD terminal device adapted to
receive the selected voltage value and a suspended particle device,
wherein the suspended particle device includes a first conducting
layer, a second conducting layer, an emulsion including a plurality
of suspended particles, which align in a predetermined pattern when
exposed to an electric field, where the emulsion positioned between
the first conducting layer and the second conducting layer, a first
connecting bus connecting the first conducting layer to the SPD
terminal and a second conducting bus connecting the second
conducting layer to the SPD terminal.
[0058] The voltage dividing device may further include a capacitor
array including a plurality of capacitors where each capacitor in
the capacitor array has a predetermined capacitance and a switch
array, connecting the capacitor array to the SPD terminal such that
each switch of the switch array connects one capacitor of the
capacitor array to the SPD terminal, wherein the controller
controls the switches of the switch array to connect at least one
of the capacitors of the capacitor array to the SPD terminal based
on the voltage level information.
[0059] The capacitor array may include 8 capacitors, and the switch
array may include 8 switches, respectively connecting each of the
eight capacitors to the SPD terminal, such that the voltage
dividing device is capable of providing a total of 256 different
voltages to the SPD terminal.
[0060] The predetermined range of distinct voltages provided by the
voltage dividing device may be sufficiently large to provide a
maximum voltage to the SPD terminal sufficient to operate a
suspended particle device of a corresponding size.
[0061] The voltage controlling device may further include an input
device adapted to provide the voltage level information from a user
of the system.
[0062] The controller may monitor an SPD voltage provided to the
SPD terminal and controls the voltage dividing device to provide
zero voltage to the SPD terminal after the SPD voltage drops a
predetermined amount below a predetermined level.
[0063] The voltage controlling device may further include an alarm,
wherein the controller provides an alarm signal that activates the
alarm after the SPD voltage exceeds the predetermined level by a
predetermined amount.
[0064] The predetermined level may be based on an average value of
the SPD voltage over a predetermined period of time. The
predetermined level may be stored in a memory of the
controller.
[0065] The voltage controlling device may further include a photo
detector adapted to monitor a level of light at the suspended
particle device, wherein the level of light at the suspended
particle is used as the voltage level information utilized by the
controller to control the voltage provided to the SPD terminal by
the voltage dividing device.
[0066] The voltage controlling device may further include an AC
power supply providing an AC voltage signal at a low frequency to
the AC terminal. The AC power supply may provide an AC voltage
signal with a frequency of at least 15 hertz.
[0067] The AC power supply may include an AC/DC converter
converting an AC voltage signal of a predetermine frequency into a
DC voltage signal, a DC motor operated by the DC voltage signal and
a generator connected to the DC motor to provide an AC voltage
signal at the low frequency.
[0068] The AC power supply may further include a plurality of solar
cells connected in parallel, at least one rechargeable battery
adapted to provide a DC voltage signal, and a converter, adapted to
convert the DC voltage signal of the battery into an AC voltage
signal with the low frequency; wherein the at least one
rechargeable battery is recharged by a recharging voltage signal
supplied by the plurality of solar cells.
[0069] The AC power supply may be in a movable support in which the
suspended particle device is mounted, such that the AC power source
moves with the suspended particle device.
[0070] The first connecting bus and the second connecting bus of
the suspended particle device may be connected to the first
conducting layer and the second conducting layer, respectively, on
one edge of the suspended particle device.
[0071] The length of the one edge of the suspended particle device
may be less than a length of another edge of the suspended particle
device such that the suspended particle device is substantially
rectangular in shape.
[0072] The bus length of the first connecting bus and the second
connecting bus, respectively, may be less than a length of the one
edge of the suspended particle device.
BRIEF DESCRIPTION OF DRAWINGS
[0073] FIG. 1 is a cross-sectional view of an SPD film;
[0074] FIG. 2 is the series equivalent circuit of the SPD film of
FIG. 1;
[0075] FIG. 3 is an example of a square piece of SPD film;
[0076] FIG. 4 is an example of a rectangular piece of SPD film;
[0077] FIG. 5 is a block diagram of a voltage controlling device
according to an embodiment of the present application;
[0078] FIG. 6 is a circuit diagram of a voltage dividing device
according to an embodiment of the present application;
[0079] FIG. 7 is a simplified AC equivalent circuit of the total
capacitance of the circuit of FIG. 6;
[0080] FIG. 8 is a graph of the light transmission through an SPD
load versus the AC voltage across the SPD load;
[0081] FIG. 9 is a table showing the physiological effects of shock
currents upon the human body;
[0082] FIG. 10 is a simplified AC equivalent circuit of a voltage
controlling device driving an SPD load under shock conditions;
[0083] FIG. 11 is a modified equivalent circuit of FIG. 10 after
the SPD load has been transformed from a series equivalent circuit
to a parallel equivalent circuit;
[0084] FIG. 12 is a simplified equivalent circuit of FIG. 11 where
the shock resistance has been combined with the equivalent parallel
resistance of the SPD load;
[0085] FIG. 13 is a final series equivalent circuit of FIG. 12
providing for a comparison of SPD load voltage with shock to normal
SPD load voltage;
[0086] FIG. 14 is a block diagram of a voltage controlling device
according to an embodiment of the present application;
[0087] FIG. 15 is a block diagram of a voltage controlling device
according to an embodiment of the present application;
[0088] FIG. 16 is a circuit diagram of a voltage dividing device
according to an embodiment of the present application;
[0089] FIG. 17 is a circuit diagram of a voltage controlling device
and an SPD load according to an embodiment of the present
invention;
[0090] FIG. 18 is a diagram illustrating a conventional position of
connecting busses in an SPD load;
[0091] FIG. 19 is an RC equivalent circuit for the SPD of FIG.
18;
[0092] FIG. 20 is a diagram illustrating positioning of conducting
busses on an SPD load according to an embodiment of the present
application;
[0093] FIG. 21 is an RC equivalent circuit for the SPD load of FIG.
20;
[0094] FIG. 22 is a diagram illustrating the placement of
conducting busses in an SPD load according to an embodiment of the
present application; and
[0095] FIG. 23 is a block diagram of an AC power supply according
to an embodiment of the present application.
[0096] FIG. 24 is a flow chart illustrating a method of controlling
voltage provided to a suspended particle device according to an
embodiment of the present application.
DETAILED DESCRIPTION OF THE INVENTION
[0097] FIG. 1 illustrates an example of a typical SPD film. The two
conducting layers 10 act like the two plates of a parallel-plate
capacitor and the emulsion 12 acts like its dielectric. The small
dots 14 represent cells (droplets) enclosing anisometrically shaped
particles such as rod-shaped particles that change their
orientation in the presence of an electric field. The capacitance
of SPD film is given by Equation 1: 1 Equation1: C spd = A d
[0098] Where .epsilon. is the permittivity of the emulsion 12, A is
the area of one conducting layer 10 and d is the distance between
the two conducting layers 10.
[0099] A voltage controlling device in accordance with the present
invention enables one to control AC voltage applied to SPD loads in
a novel, cost-effective, and safe manner. As used herein the term
"SPD load" includes SPD films, SPD light valves, and all other SPD
products that rely on the application of an electric field to
control the orientation of suspended particles. When the electric
field is zero, the suspended particles become randomly oriented
because of Brownian movement, and this randomness has the effect of
reducing or blocking the passage of light through the SPD load.
Upon application of an electric field, the particles align, usually
with their long axes parallel to the electric field, which allows
light to pass through the SPD load.
[0100] Currently available SPD films utilize AC voltages up to 200
V rms to create a maximum clear state in the SPD load. However,
much lower voltages can create an almost clear state. The value of
acceptable voltage required for a clear state depends on the
thickness of the dielectric layer, such as emulsion 12 of FIG. 1,
between conducting layers, the dielectric constant of the SPD
emulsion, and the nature of the SPD particles in the SPD emulsion.
The function of an SPD voltage controller, therefore, is to produce
an AC voltage between 0 and V.sub.max, the voltage level that
produces an acceptable level of clarity in the SPD load, for a
given application. Unless otherwise indicated, this discussion uses
60 V rms as the acceptable value of V.sub.max. It is noted that the
value of 60 V rms is selected merely for convenience and that the
voltage controlling device and methods of the present application
are not limited to use with SPD devices in which 60 V rms provides
an acceptable clear state in the SPD load. The voltage controlling
method and device invention are further defined below with
particular reference to the figures submitted herewith.
[0101] Typical SPD film has a capacitance of approximately 40 nF
per square foot, although smaller and larger values may occur with
future SPD films. This capacitance is one of the most important
parameters of SPD film because it determines how much AC current is
required by a given SPD load to produce an acceptably clear
state.
[0102] Another important parameter of SPD film is the resistance of
its conducting layers 10. These conducting layers 10 usually have a
resistance between 200 and 500 ohms per square, but the resistance
of conduction layer may vary. This resistance is the main cause of
I.sup.2R power dissipation in the SPD load. It can be shown that
the power losses of an SPD load are
[0103] Directly proportional to the square of the frequency of the
AC voltage applied to the SPD load;
[0104] Directly proportional to the square of SPD load area;
[0105] Directly proportional to the square of SPD load voltage;
and
[0106] Directly proportional to the resistance of the conducting
layers.
[0107] FIG. 2 shows an equivalent electrical circuit for SPD film.
A window including the SPD film may be of any practical size.
However, the size of individual SPD windows typically varies from
as little as 1 square foot to as many as 32 square feet, and thus,
the capacitance of the SPD load varies over a 32-to-1 range. The
resistance of the SPD load, on the other hand, has a much smaller
variation, because its value depends at least in part on which
edges of the conducting layers 10 are used for conducting (see FIG.
3). If the SPD load is square, the conducting busses 30 appear as
shown in FIG. 3, for example. In this case, the equivalent
resistance to use in FIG. 1 is given by Equation 2:
R.sub.spd=R.sub.sq Equation 2:
[0108] Where R.sub.sq. is the resistance per square of the
conducting layers 10 and typically ranges from 200 to 500 ohms.
[0109] When the SPD load is rectangular, the conducting busses 30
may run along either the longer or the shorter sides of the SPD
load. FIG. 4 illustrates an SPD load in which the busses 30 run
along the longer sides, which is the preferred location of the
busses if the main consideration in bus placement is to minimize
power losses. However, as will be discussed in further detail
below, manufacturing costs and aesthetic considerations may also be
considered in bus attachment, location, and size. For long busses
30, the resistance in the equivalent circuit of FIG. 2 is
illustrated in Equation 3: 2 Equation3: R spd = R sq L short L
long
[0110] Running the conducting busses 30 along the longer sides of
the SPD load has been preferred in the past because it results in a
more energy-efficient window since the SPD resistance in the
charging path of each active cell is decreased. That is, the path
between the respective busses 30 to the opposite edge of the SPD
load is minimized. Since the charging current for the SPD windows
must pass through this resistance, placement of the conducting
busses 30 along the longer side of a rectangular SPD load results
in smaller I.sup.2R power losses.
[0111] FIG. 5 is a block diagram of a voltage controlling device 50
according to an embodiment of the present application. The voltage
controlling device 50 of FIG. 5 is more specifically a block
diagram of a local controller for use preferably with a single
window (SPD load), or at most for use with a few SPD loads.
[0112] The voltage controlling device 50 includes an AC terminal 51
adapted to receive an AC voltage signal, a voltage dividing device
52 that divides the AC voltage signal into a plurality of distinct
voltage levels within a predetermined range. Controller 56 controls
the voltage dividing device 52 to provide a selected distinct
voltage level to the SPD terminal 54 based on voltage level
information. The SPD terminal 54 provides the selected distinct
voltage level to the SPD load 55. An input device 57 may be
provided to allow a user to input the voltage level information. A
photocell 58 may be provided to monitor a light level at the SPD
load 55 and the light level may be used as the voltage level
information.
[0113] The AC terminal 51 provides an AC voltage signal to the
voltage controlling device 50. In a simple case, AC voltage is
supplied by the AC line voltage, 120 V/60 Hz in the United States
and 240 V/50 Hz in other parts of the world. However, any AC power
source may be utilized, such as a dc-to-ac converter, commonly
referred to as an inverter, a transformer working off the mains, a
capacitive-voltage divider working off the mains, or any circuit or
device capable of delivering sufficient AC voltage of any frequency
to satisfy the SPD load requirements. In certain situations it may
be preferable to provide a separate AC power supply which will be
discussed in further detail below.
[0114] The voltage dividing device 52 may contain any electrical
device that produces a voltage drop when AC current flows through
it. Preferably, the voltage dividing device 52 divides the AC
voltage signal into a plurality of distinct voltage levels in a
predetermined range. Preferably, the voltage dividing device
divides the AC voltage into a plurality of non-continuous distinct
voltage levels in a predetermined range. In a preferred embodiment
of the present application, the voltage dividing device 52 includes
a capacitor array 60 and a switch array 62 (see FIG. 6). The
capacitor array 60 preferably includes n capacitors which will
provide 2.sup.n voltage levels to the SPD load. It is preferable to
provide an array of capacitors capable of providing a large range
of distinct voltages. For instance, a large capacitor array 60 of 8
capacitors can be properly switched via the switch array 62 to
produce 256 distinct voltage levels. A large array such as
described above, referred to as a "byte array", would be desirable
in a universal controller, that is, a controller that is capable of
controlling an SPD load of any size. For instance, if a structure
has many windows of different sizes between 1 and 32 square feet, a
byte array is preferable in that it has enough range to provide a
range of voltages which would be applicable to all SPD loads in the
structure regardless of the size of any specific SPD load. In other
words, a voltage controlling device 50 like this can be used as a
local controller for any SPD windows without regard to the area of
the window and thus is referred to as a universal controller. In
fact, a byte array has enough inherent range that it can
simultaneously control a bank of SPD windows whose aggregate area
may be hundreds of square feet.
[0115] The switch array 62 preferably includes n switches. Each
capacitor (C.sub.0 to C.sub.7) of the capacitor array 60 is
connected to one of the switches of the switch array 62. If one
switch is activated, the corresponding capacitor is connected to
the SPD load 55, preferably via the SPD terminal 54. If two
switches are activated, two capacitors in parallel are connected to
the SPD load and will drive the SPD load. In general, if n switches
are activated, there are n parallel capacitors driving the SPD
load. In the byte-array embodiment of this invention, the voltage
dividing device 52 includes 8 capacitor-switch combinations as
shown in FIG. 6. In this example, optocoupled triacs are used as
bilateral switches, however, solid-state relays, mechanical relays,
and other types of electronic or even ordinary switches may also be
used for the bilateral switches.
[0116] In a voltage dividing device 52 of the present invention,
using the capacitor array 60 and the switch array 62 allows the
voltage controlling device 50 to provide a wide range of distinct
voltage levels to the SPD load. In addition, since the voltage is
divided using a primarily capacitive device, the voltage
controlling device 50 of the present invention minimizes losses
which are common in traditional voltage controlling devices since
capacitive devices are largely lossless when used in AC circuits.
As noted above, a continuous range of voltage levels is unnecessary
for most SPD loads, thus, the capacitor array 60 which provides an
excellent means for dividing the AC voltage into a plurality of
distinct voltage levels is preferable to the continuous range
commonly provided by potentiometers of conventional voltage
controlling devices. The byte array embodiment discussed above,
provides an additional advantage in that the range of distinct
voltage levels available is large enough to be used by an SPD load
of almost any practical size.
[0117] A smaller capacitor array, however, may be preferable for
other applications. For example, a capacitor array 60 of 4
capacitors can produce 16 distinct voltage levels. Such a small
capacitor array, referred to as a "nibble array", would be suitable
for an SPD window of a specific size. For instance, if every window
in a building is exactly 16 square feet in size, then a voltage
controlling device 50 utilizing a small 4-capacitor array designed
for 16 square-foot windows would be preferable. It is important to
note that the reduced number of capacitors in the nibble array does
not in any way limit the advantages in efficiency provided by use
of a capacitor array in general discussed above. In general, byte
arrays are used in SPD applications in which SPD load size varies
widely and nibble arrays are used for SPD applications involving
the SPD windows of the same size. Although the discussion
emphasizes byte and nibble arrays, it is understood that the
voltage controlling device and methods of the present invention can
be implemented with fewer than four bits, more than eight bits, or
any number of bits in between.
[0118] The SPD terminal 54 connects the SPD load 55 to the voltage
dividing device 52. In a simple embodiment, the SPD terminal may
simply include the wires and connecting busses 30 which connect the
voltage dividing device 52 to the SPD load. More simply, the SPD
terminal may simply be embodied by the connecting busses 30
discussed above.
[0119] The controller 56 controls the voltage dividing device 52
such that a plurality of distinct voltage levels with a
predetermined range are provided to the SPD load 55 based on the
voltage level information. More specifically, in a preferred
embodiment of the present invention, outputs of the controller 56
control the on-off action of diodes D.sub.0 to D.sub.7 of the
bilateral switch array 62. When activated, these diodes close the
bilateral switches and create a parallel connection of the
activated capacitors. By combining the effects of different
capacitors (C.sub.0 to C.sub.7) a wide range of voltages are
provided to the SPD load 55 such that any desired light
transmission level can be produced in an SPD load of any size.
[0120] Generally, the controller 56 determines which bilateral
switches of the bilateral switch array 62 are active. When 8
capacitors and 8 bilateral switches are used in the voltage
dividing device 52, the total parallel capacitance of the capacitor
array 60 is given by Equation 4: 3 C T = C 7 * Bit 7 + C 6 * Bit 6
+ C 5 * Bit 5 + C 4 * Bit 4 + C 3 * Bit 3 + C 2 * Bit 2 + C 1 * Bit
1 + C 0 * Bit 0 Equation 4
[0121] where bit 7 through bit 0 represent the outputs of
controller 56. These bits may be either high or low, resulting in a
minimum nonzero capacitance of:
C.sub.T(min)=C.sub.0
[0122] When all bits are high, the maximum capacitance is
C.sub.T(max)=C.sub.7+C.sub.6+C.sub.5+C.sub.4+C.sub.3+C.sub.2+C.sub.1+C.sub-
.0
[0123] The controller 56 controls the capacitor array 60 and the
switch array 62 to produce a wide and comprehensive range of
capacitance values with only a small number of capacitors and
bilateral switches. This wide array of capacitance values can thus
be placed in series with the SPD load to provide a wide array of AC
voltage levels to the SPD load. Note that 255 distinct non-zero
values of total capacitance can be created by an array of 8
switched capacitors.
[0124] For example, the largest and most comprehensive range of
capacitance of the capacitor array 60 is obtained by using the
capacitors with the following capacitances:
[0125] C.sub.7=128C.sub.0
[0126] C.sub.6=64C.sub.0
[0127] C.sub.5=32C.sub.0
[0128] C.sub.4=16C.sub.0
[0129] C.sub.3=8C.sub.0
[0130] C.sub.2=4C.sub.0
[0131] C.sub.1=2C.sub.0
[0132] Since all capacitance values depend on the value of C.sub.0,
that value must be selected so as to create a total possible
capacitance that increases the AC voltage to the maximum desired
value (V.sub.max) and yet small enough to decrease the light
transmission of the SPD to near zero, when the smallest SPD load is
encountered. In practice, the ideal capacitance values can be
achieved by capacitor selection, by custom-made capacitors, or by a
connection of several capacitors to produce each ideal value.
However, using ideal values is not necessary. Standard commercially
available capacitors that approximate the ideal values result in
voltage controlling devices that are acceptable in most SPD
applications.
[0133] As an example of how the capacitor array 60 and the
bilateral switch array 62 can produce a comprehensive sequence of
capacitance within a desired range, if one assumes that the SPD
film, that is the SPD load in the present case, has a capacitance
of 90 nF per square foot, the best value to select for C.sub.0 is
10 nF. Then, C.sub.1=20 nF, C.sub.2=40 nF, C.sub.3=80 nF,
C.sub.4=160 nF, C.sub.5=320 nF, C.sub.6=640 nF, and C.sub.7=1280
nF. Thus, the sequence of capacitances provided by the capacitor
array 60 and bilateral switch array 62 is:
[0134] 10 nF, 20 nF, 30 nF, 40 nF, 50 nF, 60 nF, 70 nF, 80 nF, . .
. , 160 nF, 170 nF, 180 nF, . . . , 320 nF, 330 nF, . . . , 640 nF,
650 nF, . . . , 1280 nF, 1290 nF, 1300 nF, . . . , 2.530 nF, 2540
nF, and 2550 nF.
[0135] It is noted that with 8 capacitors and 8 bilateral switches,
a total of 256 digitally selectable capacitance values covering the
range of 10 nF to 2550 nF in 10-nF increments are provided. These
capacitance values correspond to a total of 256 selective voltage
levels that can be applied to the SPD load. In fact, since the
present example utilizes the byte array embodiment, the wide
variation of AC voltages is capable of controlling any SPD load of
any size as noted above.
[0136] As noted above, however, the voltage controlling device and
methods of the present application are not limited to a voltage
controlling device utilizing a voltage dividing device utilizing 8
capacitors and 8 bilateral switches. A simpler embodiment of the
invention can be used when a plurality of windows having the same
given size will be used. For instance, if five windows of 16 square
feet each are to be individually controlled, the invention could be
embodied with nibble arrays rather than byte arrays. With SPD film
that has a capacitance of 40 nF per square foot, the required array
capacitors are:
[0137] C.sub.3=470 nF
[0138] C.sub.2=220 nF
[0139] C.sub.1=100 nF
[0140] C.sub.0=47 nF
[0141] This nibble array can produce capacitances from 47 nF to 837
nF, i.e., more than enough to control the light transmission of an
SPD load with an area of 16 square feet.
[0142] To better understand the overall concept of the invention,
it is useful to examine the mathematics behind the invention. After
the controller 56 has ported the bit mask to the bilateral switches
of the switch array 62, a total capacitance of C.sub.T is placed in
series with the SPD load 55 as shown in FIG. 7. The capacitive
reactances of the total capacitance and the SPD film capacitance
are given by Equation 6 and Equation 7: 4 X T = 1 2 fC T and X spd
= 1 2 fC spd Equation 6 and Equation 7
[0143] The AC current in this circuit is given by Equation 8: 5 I =
V R spd 2 + ( X T + X spd ) 2 Equation 8
[0144] and the AC voltage across the SPD load is given by Equation
9:
V.sub.spd=1{square root}{square root over
(R.sub.spd.sup.2+X.sub.spd.sup.2- )} Equation 9
[0145] or Equation 10: 6 V spd = R spd 2 + X spd 2 R spd 2 + ( X T
+ X spd ) 2 V Equation 10
[0146] The nonlinear Equation 10 shows how the voltage dividing
device 52 creates any desired SPD load voltage. With this equation,
a suitable value of C.sub.0 can be selected, which then can be used
to define all capacitor values (C.sub.1 to C.sub.7) in the
capacitor array 60. Because of the nonlinear relation between
V.sub.SPD and the AC source voltage V, a computer solution is the
most convenient way to do a complete analysis for all SPD
loads.
[0147] Since the AC equivalent circuit of an SPD load is a series
RC circuit, one can use the figure of merit for a capacitor defined
by Equation 11: 7 Q = X spd R spd Equation 11
[0148] With smaller SPD loads, the Q is considered high (greater
than 10) and the SPD load is primarily capacitive. As the surface
area of the SPD film increases, the capacitive reactance decreases
while the resistance remains unchanged, given a square window. In
this case, the Q decreases. As one approaches larger surface areas,
i.e., greater than 16 square feet, the Q at 60 Hz decreases to less
than 10. For this reason, power losses increase nonlinearly for
larger windows.
[0149] It can be shown that the power losses increase in proportion
to the square of the surface area. For instance, a 16 square-foot
window has 256 times as much power loss as a 1 square-foot window.
For the high-Q case, the equation for current in FIG. 7 may be
approximated by Equation 12: 8 I V X T + X spd Equation 12
[0150] Since this current flows through the SPD load, the
approximate voltage across the SPD load in the high-Q case is given
by Equation 13: 9 V spd X spd X T + X spd V Equation 13
[0151] The surface area of currently available window sizes
typically varies from 1 square foot to 32 square feet. This implies
that X.sub.spd varies over a 32-to-1 range. The capacitance per
square foot depends on the thickness of the dielectric layer
between the conducting layers and also on the dielectric constant.
As a guideline for this discussion, the capacitance is
approximately 40 nF per square foot. Therefore, the approximate
capacitance range of SPD loads will be from 40 nF to 1.28
microfarads. This 32-to-1 range establishes the first preferred
parameter for a universal controller if one is desired. As
mentioned earlier, the present invention can be embodied as a local
voltage controlling device with a large capacitor array of 8 bits
or more with a view toward producing a universal controller, a
device that can produce the required voltage and current for any
SPD window between 1 and 32 square feet. On the other hand, if the
window sizes in a given application are all more or less of the
same surface area, the invention can be implemented with a smaller
capacitor array. A 4-bit array, for example, can be optimized for
use with a given window size because a 4-bit array can produce 16
distinct voltage levels, more than enough to control light
transmission of a specific window size.
[0152] In addition to providing a 32-to-1 range of total
capacitance to accommodate all SPD loads in a universal controller,
there is the issue of the voltage variation required for any given
SPD load, that is, a specific SPD window size. FIG. 8 shows a graph
of light transmission versus SPD voltage for an SPD film with a
light transmission that varies between 5 percent and 65 percent.
The values in this range are illustrative but not be construed as
defining all possible values for SPD film. Many different ranges of
light transmission are possible by varying the thickness of the SPD
film, the SPD particles, and other factors. However, the graph
illustrates these points:
[0153] At zero voltage, a minimum light transmission exists. This
is symbolized as T.sub.off..
[0154] At maximum voltage, a maximum light transmission occurs.
This is symbolized as T.sub.on.
[0155] Beyond approximately 60 V a minimal increase occurs in light
transmission.
[0156] Because of the above-described relationships, a compromise
is possible between acceptable light transmission and the voltage
required to produce such transmission. To assist in understanding
the invention, it should be understood that a universal local
controller that is capable of varying the AC voltage from 0 to
approximately 60 V rms will capture most of the useful range of
light control. Naturally, this approximate range was considered
when selecting 60 V rms as the maximum voltage provided by the
voltage controlling device because where the SPD load voltage is
increased above the 60 V rms level, there is a minimum increase in
the clarity of the SPD load. In some applications, slightly more or
slightly less voltage might be desired or acceptable.
[0157] As noted previously, the human eye is unable to detect small
changes of light transmission. For instance, the eye cannot discern
a change of 1 percent in light transmission. Rather, it takes
changes of approximately 10 to 20 percent before the eye can detect
changes in light level. Therefore, a controller that can produce 8
distinct voltage levels between 0 and 60 V provides a satisfactory
range of adjustment. Specifically, a voltage controlling device
that can produce the following voltages is satisfactory as a
universal controller:
[0158] 0, 7.5, 15, 22.5, 30, 37.5, 45, 52.5, 60 V
[0159] These being the case, one can now see why an 8
capacitor-switch combination is a satisfactory solution for a
universal local controller. To begin with, there is the preferred
parameter of a 32-to-1 range to accommodate any SPD load size.
Then, as noted above, a specific SPD load is satisfactorily
activated when 8 distinct voltage levels are used. The product of
these preferred parameters is 8 times 32, or 256, which is the
total number of distinct states that a voltage dividing device with
an 8 capacitor array and 8 switch array has.
[0160] As mentioned earlier, the foregoing discussion should not be
construed as limiting the voltage controlling device of the present
invention to a controller realized in 8-bit arrays. Depending on
the application and user acceptance, smaller arrays with larger
increments between total capacitance values may be acceptable.
Likewise, there might arise a situation where a 10-bit array might
be desired for larger SPD loads. At the other extreme is the 4-bit
array with its 16 distinct states, which is more than enough range
to allow a design for a specific window size.
[0161] The voltage controlling device 50 of the present invention
is useful in preventing the user from being shocked. Although SPD
windows use low current and should not pose any serious shock risk,
it is still important to use properly designed electronics to
control these SPD windows. As discussed earlier, currently
available SPD film requires only 1 mA per square foot to provide a
clear state. With this mind, let us now consider the issues
surrounding potential electrical shock.
[0162] FIG. 9 is a table of Shock Physiological Effects. Notice
that currents up to 8 mA are considered safe because a person can
let go at will since muscular control is not lost. Dry skin has a
resistance in the hundreds of kilohms, whereas wet skin may have a
resistance as low as 1000 ohms. Because the SPD load voltage is
relatively low, the danger of electrical shock exists only when wet
skin makes contact with exposed busses 30 or the conducting layers
10. Although the busses 30 and conducting layers 10 are insulated,
there is a need for some form of shock protection in some
applications where window breakage occurs. Even in this situation,
the insulation on the busses 30 and conducting layers 10 should
remain intact to prevent shock. Nevertheless, notwithstanding the
above, various forms of shock protection are included in the
voltage controlling device of the current invention.
[0163] FIG. 10 shows an AC equivalent circuit of one embodiment of
the voltage controlling device 50 of the present invention driving
an SPD load, which is some distance away. If the SPD film is
damaged by glass breakage or by piercing or cutting of any kind, a
potential may exist for an electrical shock. R.sub.SHOCK represents
the skin resistance of a person. The ground return on R.sub.SHOCK
may be either through a ground fault or through a direct return on
the neutral side of the line. At this point in the discussion, a
voltage V.sub.WS, the SPD load voltage with shock when the shock
current is 5 mA or more should be determined. To this end, one
begins by using a transformation of the SPD series equivalent
circuit into its parallel equivalent circuit using Equations 13-15:
10 Q = X spd R spd R P = R spd ( 1 + Q 2 ) X P = X spd ( 1 + 1 Q 2
) Equation 13 - 15
[0164] The first equation determines the figure of merit Q of the
SPD load 55. The second equation determines the parallel equivalent
effect of the series equivalent resistance. The third equation
determines the parallel equivalent reactance of the series
equivalent reactance. These transformations imply the modified
equivalent circuit of FIG. 11. In this figure, the two resistances
are in parallel and may be reduced to a single resistance R.sub.PP
shown in FIG. 12. In a final transformation, the parallel branches
of R.sub.PP and X.sub.P are transformed into a series equivalent
circuit using Equations 16-18: 11 Q PP = R PP X P R S = R PP 1 + Q
PP 2 X S = X P 1 + 1 / Q PP 2 Equations 16 - 18
[0165] These final transformations imply the equivalent circuit of
FIG. 13. In this highly simplified form, it is relatively easy to
calculate the effect of the shock resistance. The result is a
series RC circuit current with shock current I.sub.WS given by
Equation 19: 12 I WS = V R S 2 + ( X T + X S ) 2 Equation 19
[0166] Referring to FIG. 7, one can see that the normal value of
current is given by Equation 20: 13 I N = V R spd 2 + ( X T + X spd
) 2 Equation 20
[0167] The most convenient way to compare the SPD load current with
shock to the normal current is with a computer simulation that
includes a shock resistance that varies from 1000 ohms to 12,000
ohms for any SPD load. The reason for 12,000 ohms being chosen as
the upper limit is because the preferred embodiment of the
invention limits the maximum voltage to 60 V rms, which implies a
maximum possible shock current of 5 mA when the shock resistance is
12,000 ohms.
[0168] It is to be understood that the capacitor array 60 reduces
the input voltage from the AC terminal 51 to vary the SPD load
voltage because its impedance is in series with the SPD load. In
other words, the AC current flows through this impedance, resulting
in a reduced SPD load voltage. Since the controller 56 determines
the value of this impedance, it effectively determines the SPD load
voltage. In a preferred embodiment of the present application, an
SPD load voltage is monitored by the controller 56. A normal value
of SPD load voltage provided by the voltage controlling device is
sampled and stored in a memory (not shown) of the controller 56 in
a manner well understood by one of ordinary skill in the art. This
normal value is used as a benchmark for determining the presence of
any shock current. Alternatively, normal SPD load voltage levels
may be preloaded into the memory to establish the benchmark. The
appearance of either ground fault or direct-contact fault reduces
the value of SPD load voltage to a level that is noticeably less
than the normal SPD voltage. The controller 56 continuously
monitors the SPD load voltage and compares it to the normal value.
The controller 56 can quickly determine when the SPD load voltage
differs significantly from its normal value and can take
appropriate action to shut down the power, that is to reduce the
SPD load voltage to 0, in the case of a large drop in SPD
voltage.
[0169] Turning now to a discussion of how the current invention
will shut off the power when a shock current equal to or greater
than 5 mA appears, as noted previously, the SPD load voltage is
continuously sampled by the controller 56. More specifically, the
controller samples the SPD load voltage via an analog-to-digital
converter that can be included in the controller which transforms
the AC SPD load voltage signal into an 8 bit digital signal that
can be used by the controller 56. In a typical embodiment of the
invention, the maximum voltage applied to any SPD load of any size
is limited to approximately 60 V rms to minimize energy losses in
the resistance of the conducting layers 10 as well as any
resistance in the voltage controlling device 50 itself. To detect
the SPD load voltage, one can use its average value, rms value, or
peak value. Because the peak value is well defined and easy to
measure, the preferred embodiment of the voltage controlling device
of the present invention will use the peak value, with the
understanding that any characteristic of the SPD load that is
related in a one-to-one correspondence to the rms value may be
used. The peak voltage corresponding to 60 V rms is given by
Equation 21:
V.sub.P{square root}{square root over (2)}(60 V)=85 V Equation
21
[0170] The digital output of an AD converter typically has at least
8 bits. If one uses an AD converter with an 8-bit output, the least
significant bit (LSB) at the SPD-load sample point is given by
Equation 22: 14 LSB = 85 V 255 = 0.333 V Equation 22
[0171] This represents the minimum detectable change in SPD load
voltage.
[0172] Returning to FIG. 10, note the following. Under normal
conditions, R.sub.SHOCK is infinite, that is, there is no shock
condition. After the user makes an adjustment via the input device
57, for example, to alter the clarity of the SPD load, the SPD
voltage is relatively stable. The SPD load voltage after
stabilization is the normal SPD load voltage, symbolized by
V.sub.N, which the controller 56 stores in its memory. If any
situation should arise where R.sub.SHOCK decreases because the SPD
film has been pierced or cut, then the SPD load voltage with shock,
symbolized by V.sub.WS, will decrease because of the loading effect
that occurs when additional current flows through the voltage
dividing device 52. With proper design, the decrease in SPD load
voltage is large enough with 5 mA of shock current to be detectable
by the controller 56. The controller 56 is continuously monitoring
the SPD load voltage, however, and comparing it to the normal SPD
voltage stored in its memory. If a shock current equal to or
greater than 5 mA should occur, the controller 56 will detect this
condition and immediately shut off the power to the SPD load.
[0173] As noted previously, the resistance of dry skin is typically
several hundred thousand ohms, which means very low shock currents
exist with dry skin. However, when the skin is perspiring or wet,
skin resistance may drop to as low as 1 kilohm. In a preferred
embodiment of the current invention, the maximum SPD load voltage
is limited to 60 V. Therefore, the critical or highest skin
resistance that can produce a shock current of 5 mA is given by
Equation 23: 15 R critical = 60 V 5 mA = 12 kilohms Equation 23
[0174] Any resistance less than 12 kilohms may be dangerous because
it can produce a shock current in excess of 5 mA. For instance, a
skin resistance of 2 kilohms produces a shock current of 5 mA with
an SPD load voltage of only 10 V rms. Therefore, it is necessary to
determine the values of V.sub.N and V.sub.WS, and then calculate
the difference between them, which is symbolized as DIFF. The value
of DIFF in LSB (least significant bit of the AD converter) must be
large enough to ensure reliable detection of a 5-mA shock under all
operating conditions. For instance, with the equations discussed
earlier, the following are the results for a 16 square-foot window,
a skin resistance of 5 kilohms, and a shock current of 5 mA:
[0175] V.sub.N=30.8 V rms=43.5 Vpeak
[0176] V.sub.WS=25.7 V rms=36.3 Vpeak
[0177] DIFF=7.2 V=21.6 LSB
[0178] AD converters typically are accurate and reliable to within
0.5 LSB, so the foregoing difference of 21.6 LSB is easily
detectable by the controller. Additional calculations show that
largest deviations from normal SPD voltage with a shock current of
5 mA occur for smaller window sizes and lower skin resistances.
With larger window sizes like 32 square feet, DIFF becomes smaller
but is still detectable because it is more than 2 LSB under any
operating condition where the shock current is 5 mA. The conclusion
is that the local controller can detect any shock current equal to
or greater than 5 mA, no matter what the window size or skin
resistance.
[0179] The current invention has an additional benefit in the area
of security. If a burglar or other intruder breaks an SPD window to
enter a home, office, vehicle, or other area, the capacitance of
the SPD load changes and causes the window current to change. This
change in window current is detectable based on the change in SPD
load voltage using the same mechanism as that used to detect the
presence of a shock current described above. The difference is that
instead of looking for a drop in SPD load voltage, the controller
56 detects an unwanted increase in SPD load voltage. When a
substantial increase in SPD load voltage above the baseline level
discussed above is detected, the controller 56 can send a signal to
a burglar-alarm (not shown) to warn of the intrusion.
[0180] The input device 57 is any kind of tunable resistance or
other means of producing a DC voltage suitable for user input to an
analog-to-digital converter, hereafter referred to as an AD
converter(not shown). Examples of such a tunable resistance are
potentiometers that are rotary, slide, thumbwheel, finger-pressure,
etc. Either acting alone or as part of a voltage divider, the input
device 57 allows the user to control a DC voltage that varies from
0 to V+, where V+ is the maximum allowable voltage to the AD
converter. In a typical embodiment of the invention, this voltage
is +5 V, the same voltage used to power the controller 56.
[0181] The AD converter may be incorporated in the controller 56 as
shown in FIG. 5, or the AD converter may be a stand-alone device
that works with a controller 56 that does not have built-in AD
converters. In either case, when an 8-bit controller is used to
embody the invention, the AD converter will have a digital output,
typically 8 bits when 8 capacitors and bilateral switches are used,
but not necessarily restricted to 8 bits. For instance, some AD
converters produce 10-bit outputs. To use such an AD converter with
an 8-bit controller, the controller 56 can be programmed to divide
the decimal equivalent of the 10-bit number range by 4 to get an
8-bit range. In a preferred embodiment of the voltage controlling
device 50 according to the present invention, the input device 57
creates a one-to-one correspondence between user input and the
total capacitance value of the voltage dividing device 52. In this
way, the user is able to tune in whatever total capacitance
produces the desired light transmission through the SPD load
55.
[0182] The controller 56 is typically any microcontroller that has
an arithmetic-logic unit (ALU), read-only memory (ROM),
random-access memory (RAM), and input/output (I/O) ports. In FIG.
5, AD converters are included in the controller 56, but in the
present invention these may be stand-alone units working in
conjunction with a controller.
[0183] The controller 56 of FIG. 5 is programmed to sample the
voltage produced by the input device 57 and produce a digital
equivalent. With an 8-bit AD output, this will be a number between
0 and 255, spaced in intervals of 1, that is, 0, 1, 2, 3, . . . ,
255. This user-selected number is then ported to the controller
output where it activates the bilateral switches of the bilateral
switch array 62, which in turn, determines the total capacitance
value of the voltage dividing device 52. This capacitance will then
interact with the specific SPD load and result in a final SPD load
voltage being greater for smaller SPD loads, and smaller for larger
SPD loads. In the current invention, the quantity C.sub.0 can be
selected to accommodate a very large range of SPD loads. In fact,
there is theoretically no limitation on the range of SPD loads that
can be controlled because one can increase the number of capacitors
and bilateral switches to whatever number is needed to satisfy any
conceivable range of SPD loads. For example, one can use an array
of more than 8 capacitors and bilateral switches. If one uses 10
capacitors and bilateral switches, the total capacitance can vary
from 0 to 1023C.sub.0, which is a huge range capable of application
with any SPD load with a film surface area between 1 square inch
and 100 square feet.
[0184] In another embodiment of the voltage controlling device of
the present application a photocell 58 as illustrated in FIG. 5 may
be added. The photocell 58 may be any kind of light-detecting
device such as a photoresistor, photodiode, or other such device
that can deliver a voltage between 0 and V+, defined as the maximum
allowable voltage of an AD converter. The controller 56 can be
programmed to automatically turn off the power to the SPD load when
the incident light detected by the photocell 58 approaches zero. In
other words, to conserve power the microcontroller can turn off the
power at night and allow the windows to go into the dark mode. This
saves energy.
[0185] The light response of the photocell 58 may be stored in the
memory of the controller 56. The controller 56 can be programmed to
respond to various light levels during the daytime. When more
sunlight strikes the photocell 58, the controller 56 can alter the
capacitor array 60 via the switch array 56 to darken the SPD
windows. In this way, automatic control of the SPD windows can be
achieved.
[0186] To this point, the present application has concentrated on a
voltage controlling device utilized in controlling voltage provided
to one, or a few SPD loads. In the simplest case, the AC voltage
provided to the controller is provided from the main lines.
However, as noted above, in certain applications, it may be
advantageous to provide a separate AC power supply, or source, to
the voltage controlling device of the present invention. For
example, when attempting to control many SPD loads simultaneously
from a single voltage controlling device, a so called master
controller, a separate AC power source operating at a frequency
lower than 60 Hz may be provided. Because an SPD load 55 acts like
a parallel-plate capacitor, its capacitive reactance is inversely
proportional to frequency. Therefore, the SPD window current is
directly proportional to frequency. If the AC voltage signal
provided to the voltage controlling device 50 of FIG. 5 has a
frequency of 30 Hz instead of 60 Hz, the window current drops in
half. It is possible to reduce the frequency even lower, provided
the frequency remains high enough to avoid window blinking, which
occurs at approximately 10 Hz. The idea of using a very low
frequency such as 15 Hz has major implications for power
efficiency, cost advantages, simplified controller design, and a
number of other benefits.
[0187] The minimum frequency of 15 Hz is a somewhat unexpected
result. It is well known that movies are filmed at 24 frames per
second and that the use of two-blade shutters increases the
effective flash rate of movies to 48 frames per second, which is
considered the minimum acceptable flash rate to avoid flicker. SPD
particles respond twice per cycle to the AC voltage: once during
the voltage transition from positive to negative, and a second time
during the transition from negative to positive. Since there are
two voltage transitions per cycle, the effective flash rate for a
15 Hz drive is 30 flashes per second. While this is lower than the
known minimum flash rate utilized in movies to prevent flicker,
flicker does not occur in the SPD load. Movies go completely dark
between flashes, however, the clarity of an SPD load does not
decrease to 0 between the negative to positive and positive to
negative transitions of the AC voltage. The orientation of an SPD
particle decays slowly, rather than instantaneously, because of
Brownian motion toward a random state. This randomizing decay has a
long enough time constant such that the SPD film does not go dark
during a voltage transition. Instead, the SPD particles have only a
small amount of time to randomize or decay between voltage
transitions. The net effect observed by experimentation is that
flicker in the SPD load is noticeable only when the driving
frequency is as low as 10 Hz. Therefore, 15 Hz is sufficiently
above the flicker threshold to safely avoid any flicker with SPD
loads. Naturally a slightly lower frequency may also be utilized,
provided it does not drop below the flicker threshold.
[0188] FIG. 14 shows one embodiment of a voltage controlling device
with its own AC power source 142 of 120 V and 15 Hz. For the sake
of convenience, the same reference numbers will be used for
elements of the voltage controlling device that correspond to the
common elements of voltage controlling device 50 of FIG. 5. The
conversion from 60 Hz to 15 Hz is accomplished in two stages.
First, a first converter 143, i.e., an ac-to-dc converter, changes
the input line voltage to a DC voltage. The DC output of the first
converter 143 is used to drive a second converter 144, i.e., a
dc-to-ac converter, that produces 120 V at the lower frequency of
15 Hz. This lower frequency voltage signal may then be supplied to
the voltage controlling device 50 illustrated in FIG. 5 described
above. In this embodiment, the SPD load 55 of FIG. 5 may be a
plurality of SPD loads, such as several SPD windows, for
example.
[0189] Alternatively, in very large office buildings, for example,
it might be cost effective to use a small motor-generator
combination 150 as shown in FIG. 15 to produce the 120 V AC at a
frequency of 15 Hz. In this embodiment, the AC power source 142
includes motor generator combination 150 which includes a motor 152
powered by the line voltage which in turn is used to power a
generator 154 which produces the 120 V AC voltage at 15 Hz. This
frequency is high enough to avoid window blinking and is low enough
to reduce the maximum window current by a factor of four. The
benefit of reducing window current by a factor of four is a
reduction in the size of components and in the complexity of
controller design. Stated another way, a given amount of window
current can control four times as much window area when 15 Hz is
used instead of 60 Hz. The low frequency AC voltage can then be
supplied to the voltage controlling device 50 illustrated in FIG. 5
as the AC voltage signal.
[0190] With a low-frequency AC voltage source, a voltage
controlling device can control a large number of office windows
with high power efficiency. For instance, given a large office with
40 windows measuring 8 ft by 4 ft each, the total window area is
1280 square feet. A voltage controlling device for all of these
windows could be implemented with a voltage dividing device 52 such
as that included in the voltage dividing device 50 illustrated in
FIG. 5 utilizing a 6-bit capacitor array 162 and switch array 164
shown in FIG. 16. The top bilateral switch of the bilateral switch
array 162 connects the 120 V and 15 Hz and the remaining capacitors
(4.7 nF, 10 nF, 22 nF, 47 nF, and 100 nF) to produce the different
voltage levels. The capacitor array 162 and the switch array 164
will produce 64 distinct voltage levels ranging from 0 to 120 V.
This would provide a satisfactory control of light transmission for
1280 square feet of SPD windows. Since capacitors produce the
voltage levels, the invention has the benefit of eliminating the
large variable transformers that conventional controllers use.
Capacitors are more efficient than transformers since capacitors do
not have the winding and core losses that transformers have.
[0191] For shock protection on the individual windows receiving the
120 V at 15 Hz, one can use an alternative method of
shock-protection. Because the required SPD load currents are four
times smaller at 15 Hz than they are at 60 Hz, one can add a
current-limiting resistor 170 in series with each individual window
as shown in FIG. 17. For windows up to 16 square feet, R.sub.limit
has a value of approximately 24 kilohms. With a 120 V source, the
maximum current under short circuit conditions is 5 mA. Therefore,
if the window is broken, the maximum possible shock current is 5
mA. Under normal operating conditions, the voltage available to the
SPD window will be a minimum of 60 V. For larger windows up to 32
square feet, the limiting resistor can be reduced to 15 kilohms.
This produces an operating voltage of at least 60 V while ensuring
that the maximum shock current is less than 8 mA. This use of
current-limiting resistors on large SPD windows up to 32 square
feet is feasible only at lower frequencies such as 15 Hz because it
is only at these lower frequencies that the SPD currents are small
enough to allow the use of current-limiting resistors on larger
windows.
[0192] As noted previously, the placement of the busses 30 on the
SPD load may be reconsidered to take into account factors other
than power efficiency. FIG. 1 shows a cross-sectional view of SPD
film with the two conducting layers 10, hereafter referred to as
the indium-tin-oxide (ITO) layers. These ITO layers may have a
sheet resistance in the range of 50 to 500 ohms with thicknesses of
100 to 10 nm. Basically, they form the plates of a parallel-plate
capacitor. Each minute SPD cell inside an SPD film acts like a
differential capacitor. Since the sheet resistance measured in
squares is in series with each of the differential capacitors, we
can visualize the SPD film as a large number of extremely small
series RC circuits. By integrating the effect of all these
distributed series RC circuits, we can arrive at a single lumped
constant RC circuit to represent the SPD film. With the values of R
and C of this lumped-constant circuit in mind, one of ordinary
skill in the art would be readily able to follow the teachings
above and provide an AC generator and controller to drive SPD
loads.
[0193] The state of art has been to rely on busses 30 that are on
opposite sides of the SPD film as shown in FIG. 18. The bus 180 on
the left is on the top ITO and the bus on the right 180a is on the
bottom ITO. The reason for using this configuration is because the
total charging resistance for any differential capacitor is a
constant, no matter where the cell is located in the emulsion
layer. FIG. 19 illustrates this point out clearly. In other words,
the total charging resistance for any cell is given by Equation
24:
R.sub.total=R.sub.1+R.sub.2 Equation 24
[0194] For a given size window, R.sub.total has the same value for
any cell because the same total number of squares of resistance are
in the charging path. The advantage of the opposite-side busses
180, 180a is that a constant charging resistance for each cell
implies a uniform response throughout the SPD film. The
disadvantage is that the connecting wires to an SPD window may be
as much as 4 ft apart on and 8 foot.times.4 foot window at the
entry points of connection to the SPD film.
[0195] The first bus improvement afforded by this invention is to
locate busses, such as 200, 200a, on the same side of the SPD film
or load, as shown in FIG. 20. In such an arrangement the entry
connecting wires to the window are fractions of an inch apart, a
decided advantage during installation. But this configuration will
no longer guarantee a uniform response because the charging path
for the different cells will be different as shown in FIG. 21.
R.sub.1 and R.sub.2 will each be smaller when the differential
capacitance is closer to the busses because fewer squares of
resistance are in the charging path. This implies that the cells on
the left receive more voltage than the cells on the right. In other
words, the response becomes non-uniform. However, computer
simulation and lumped-constant equivalent breadboards of an 8
ft.times.4 ft film with sheet resistance of 350 ohms per square and
capacitance of 40 nF per square foot, and with busses on the longer
and conventional 8 ft. sides demonstrating that the decrease in
voltage moving from the bussed side to the unbussed side is less
than 1 percent when operating at 60 Hz. As stated earlier, the
human eye cannot detect changes in light transmission of less than
10 percent. Therefore, using busses on the same side produces a
response that appears uniform to the human eye.
[0196] In another embodiment of the present invention, busses may
be positioned on the shorter side rather than the longer side of
rectangular SPD load. As discussed above, the only reason for using
busses on the longer side was to minimize the number of squares in
the charging path of each cellular capacitance. However, the power
losses of currently available SPD film are so small compared to the
power losses in controller circuits that busses on the shorter side
produce a negligible decrease in the overall power efficiency of a
combined controller-window device. Again, the proof that using the
shorter bus is acceptable was to use both computer simulation and
breadboards of an 8 ft.times.4 ft film with busses on the shorter
and unconventional 4 ft sides. In this case, the decrease in
cellular voltage from the bussed to the unbussed sides was less
than 5 percent, too small for the eye to detect any non-uniformity
in window transmission.
[0197] Another embodiment of the present invention uses very small
busses, that is, rather than run a bus along as much as a 4-ft
length, the bus is run along a much smaller length such as 1 inch
or less. The bus length is not critical, so the use of 1 inch is
not to be construed as essential for this invention. A larger or
small bus may be used. In fact, bus lengths as small as 0.25 inches
have proved to be entirely satisfactorily in bread-boarded models.
FIG. 22 shows the idea of using very small busses, 220, 220a, on
the same side of the SPD film. The manufacturing advantages of this
small-bus, same-side configuration are impressive because the hand
labor in attaching the busses is almost eliminated. In addition to
the manufacturing advantages, small busses on the same side have
another advantage: they eliminate the need for an aesthetic
covering that would be required with longer busses.
[0198] In FIG. 22, the worst-case response for cellular capacitance
charging occurs for those cells in the upper right-hand corner
because this is the greatest distance between the bus and the cell.
Computer models and bread-boarded devices show that small busses on
the same side are entirely satisfactory because the response is
uniform to the human eye throughout the SPD film. Although the
small busses, 220, 220a are shown in the lower left corner in FIG.
22, their location is not restricted. These busses can be located
anywhere on the periphery. For instance, with an automobile window
the small busses can be located on the bottom horizontal and the
left or right vertical, as needed. The freedom to locate the small
busses wherever convenient along the periphery is a decided
installation advantage.
[0199] SPD loads that are movable or sliding present an additional
wiring problem and are addressable by the present invention. With
same-side small busses, such as 220, 220a, located at one corner of
an SPD window, one can use retractable wiring that fits in the wall
space. This is one approach that will allow AC power to be
delivered to a sliding for movable SPD window.
[0200] FIG. 23 shows another embodiment of a voltage controlling
device according to the present invention. In this embodiment at
least one rechargeable battery 231 is used to provide electrical
power for the SPD load. A group of miniature solar cells 232
convert solar energy into electrical energy. The typical solar cell
produces a small voltage. By placing these solar cells in series,
one can obtain a high enough voltage to charge one or more
batteries. By using rechargeable batteries, power will be available
on overcast days when it is most needed to keep the SPD windows in
the clear state. The voltage out of the batteries is converted by
the dc-to-ac converter 234 to produce the required AC voltage for
the movable SPD window. Because the solar cells 232, at least one
battery 231, and remaining electronics can be designed into the SPD
window casing, there is no need to connect any external wires to
the busses. In other words, the SPD window of this embodiment is
self-powering.
[0201] In one embodiment of the invention, silicon solar cells are
used. A typical silicon solar cell produces an output voltage of
approximately 0.6 V. Output currents depend on the physical
construction of the solar cell. Current may vary from less than 50
mA to more than 5 A. Since SPD windows require only small currents
in the vicinity of 1 mA per square foot, one can use miniature
solar cells in series to obtain higher voltage. For instance, with
15 silicon cells in series, the output voltage is 9 V, enough to
charge a rechargeable 9-V battery. The dc-to-ac converter 234 may
be an inverter of high efficiency to avoid excessive battery drain
current Alternatively, a Wien-bridge oscillator, a relaxation
oscillator, or any other oscillator circuit plus a step-up
transformer or inductive method of stepping up the voltage can be
used. Furthermore, with SPD films of the future holding out the
promise of much lower AC operating voltages, solar-powered SPD
windows with simple electronics, very low cost, and high efficiency
are likely to evolve.
[0202] A method of controlling voltage provided to a suspended
particle device is described with reference to FIG. 24. In step
S240, an AC voltage signal from an AC power source. At step S242,
the AC voltage signal is divided into a plurality of distinct
voltage levels within a predetermined range. At step S244, the
dividing step is controlled to provide a selected voltage level of
the plurality of distinct voltage levels to an SPD terminal
connected to the suspended particle device based on voltage level
information.
[0203] The method of FIG. 24 is substantially similar to that
utilized by voltage controlling device 50, for example, described
herein, and therefore, there is no need to discuss the method in
further detail.
[0204] Each of the patents and other references noted herein is
incorporated into the present specification to the degree necessary
to comprehend the invention.
[0205] Numerous additional modifications and variations of the
present invention are possible in view of the above-teachings. It
is therefore to be understood that within the scope of the appended
claims, the present invention may be practiced other than as
specifically described herein.
* * * * *